Over the past decade there has been a significant focus of research on the development of micro-total-analytical systems which are referred to as μ-TAS or lab-on-a-chip devices. This technology is based on the use of a series of microfluidic channels or microchannels for the movement, separation, reaction, and/or detection of various chemicals (e.g. proteins, DNA, chemical compounds, etc.). Movement of the fluids within the microchannels can be effected by means of applied pressure gradients or electric fields applied along the length of the channel. In the latter phenomenon, known as electroosmosis, the larger the magnitude of the applied electric field or the greater the surface charge, the greater the induced fluid velocity.
The development of lab-on-a-chip devices has progressed rapidly, however there are still several issues that must be resolved. Most of these issues stem from the need to control flow and/or immobilize reagents within the fluid flow channels. Such control or immobilization can be achieved through the modification of the surface charges. Since electroosmotic flow is a result of surface charge, the ability to change the charge is critical to the optimization of lab-on-a-chip devices. One method for controlling and changing the surface charge is through the use of wall coatings, which has been shown to increase, decrease, or even reverse the electroosmotic flow in specific regions of the channels. Unfortunately, the use of wall coatings complicates and increases the costs of the fabrication process. Moreover, such coatings may become unstable over time.
Surface charge modification of the microchannels is also used to selectively bind molecules such as DNA, proteins, molecules, etc. therein. Such bound molecules can then be used in devices that function as chemical sensors, DNA or protein microarrays, etc. Current reported methods for binding proteins require a rather complex soft lithography technique. Another process uses a two-step lamination technique or a two-step bovine serum albumin (BSA) blocking technique to pattern proteins. These procedures tend to complicate the fabrication process.